1. Field of the Invention
The present invention relates to an electronic part comprising an electric insulating material made of polyimide as a structural component and a process for manufacturing the electronic part. More particularly, the present invention relates to an electronic part comprising an electric insulating material having excellent heat resistance and low dielectric constant as a structural component, and a process for manufacturing the electronic part.
2. Description of the Background Art
Semiconductor devices such as an LSI (large scale integrated Circuit) which are used for various electric parts and electronic parts are making steady progress in high integration, multifunction, and high performance by virtue of the progress in fine process techniques. Consequently, circuit resistance (hereinafter called "parasitic resistance" from time to time) and the capacity of a capacitor (hereinafter called "parasitic capacity") increase. Along with these increases in the parasitic resistance and capacity, there are increases in not only the power consumption but also in the time delay in response to an input signal. This is the primary cause of low signal speed in semiconductor devices, giving rise to the problem to be solved.
Minimizing the above parasitic resistance and capacity has been proposed as a measure to prevent such a decrease in the signal speed. One method that has been proposed is to cover spaces between wires or the periphery of wires with an insulation film having a low dielectric constant to decrease the parasitic resistance, thereby achieving a high speed signal.
A specific example is to replace an inorganic film formed of silicon dioxide (SiO.sub.2) which is a conventional insulating film used between layers with an organic film having a low dielectric constant. The material for such an organic film must have excellent electric insulation and a low dielectric constant to correspond to a high speed signal in semiconductor devices. Such a material must also possess excellent heat resistance to withstand heat treatment (heating step) in a thin-film forming step in a process for manufacturing a mounting substrate or in the stages of chip joining and pin binding.
Here, fluororesins such as polytetrafluoroethylene (PTF) are known as the organic film materials having a low dielectric constant. These fluororesins are, however, insoluble in common organic solvents. Other drawbacks of the fluororesins are their inferior workability and poor handling characteristics. In addition, the fluororesins have an economic disadvantage because the resins must be formed into a specific formulation to be applied for diverse applications of electronic parts. Therefore, the fluororesins are used in very limited fields.
Also, polyimide resins are widely known as high heat-resistant organic materials. There is a known polyimide resin with particularly high heat-resistance which is obtained by reacting 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene used as an amine compound and a pyromellitic acid dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-diphenylsulfontetracarboxylic acid dianhydride, or 3,3',4,4'-benzophenontetracarboxylic acid dianhydride used as an acid anhydride (J. Polymer Sci., Part A: Polymer Chemistry, Vol. 31, 2153-2163(1993)).
Although these polyimide resins have high heat resistance, their dielectric constant is in the range from 2.9 to 3.5 which cannot yet satisfy the requirements for the layer insulation film used for semiconductors with high speed signal transmission capability.
Another problem with such a polyimide resin is its poor solubility in organic solvents. Not only it is difficult to prepare a uniform thin film from the resin, but also the resin exhibits only poor processablity and handling characteristics.
The present invention has been achieved in view of this situation. Specifically, the present invention has been completed based on the finding that a polyimide obtained by reacting a specific aromatic diamine compound and a specific aromatic tetracarboxylic acid compound has a low specific dielectric constant and excellent heat resistance and solubility in a solvent.
Accordingly, an object of the present invention is to provide an electronic part comprising an electric insulating material formed of polyimide having a low dielectric constant (specific dielectric constant), high heat resistance, as well as superior solubility in various solvents and excellently balanced properties.